Entanglement of two quantum memories via fibres over dozens of kilometres

Yong Yu; Fei Ma; Xi-Yu Luo; Bo Jing; Peng-Fei Sun; Ren-Zhou Fang; Chao-Wei Yang; Hui Liu; Ming-Yang Zheng; Xiu-Ping Xie; Wei-Jun Zhang; Li-Xing You; Zhen Wang; Teng-Yun Chen; Qiang Zhang; Xiao-Hui Bao; Jian-Wei Pan

doi:10.1038/s41586-020-1976-7

Entanglement of two quantum memories via fibres over dozens of kilometres

Nature. 2020 Feb;578(7794):240-245. doi: 10.1038/s41586-020-1976-7. Epub 2020 Feb 12.

Authors

Yong Yu^#^{1

2

3}, Fei Ma^#^{1

2

3

4}, Xi-Yu Luo^{1

2

3}, Bo Jing^{1

2

3}, Peng-Fei Sun^{1

2

3}, Ren-Zhou Fang^{1

2

3}, Chao-Wei Yang^{1

2

3}, Hui Liu^{1

2

3}, Ming-Yang Zheng⁴, Xiu-Ping Xie⁴, Wei-Jun Zhang⁵, Li-Xing You⁵, Zhen Wang⁵, Teng-Yun Chen^{1

2

3}, Qiang Zhang^{6

7

8

9}, Xiao-Hui Bao^{10

11

12}, Jian-Wei Pan^{13

14

15}

Affiliations

¹ Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.
² Department of Modern Physics, University of Science and Technology of China, Hefei, China.
³ CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China.
⁴ Jinan Institute of Quantum Technology, Jinan, China.
⁵ State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai, China.
⁶ Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China. qiangzh@ustc.edu.cn.
⁷ Department of Modern Physics, University of Science and Technology of China, Hefei, China. qiangzh@ustc.edu.cn.
⁸ CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China. qiangzh@ustc.edu.cn.
⁹ Jinan Institute of Quantum Technology, Jinan, China. qiangzh@ustc.edu.cn.
¹⁰ Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China. xhbao@ustc.edu.cn.
¹¹ Department of Modern Physics, University of Science and Technology of China, Hefei, China. xhbao@ustc.edu.cn.
¹² CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China. xhbao@ustc.edu.cn.
¹³ Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China. pan@ustc.edu.cn.
¹⁴ Department of Modern Physics, University of Science and Technology of China, Hefei, China. pan@ustc.edu.cn.
¹⁵ CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China. pan@ustc.edu.cn.

^# Contributed equally.

PMID: 32051600
DOI: 10.1038/s41586-020-1976-7

Abstract

A quantum internet that connects remote quantum processors^1,2 should enable a number of revolutionary applications such as distributed quantum computing. Its realization will rely on entanglement of remote quantum memories over long distances. Despite enormous progress^3-12, at present the maximal physical separation achieved between two nodes is 1.3 kilometres¹⁰, and challenges for longer distances remain. Here we demonstrate entanglement of two atomic ensembles in one laboratory via photon transmission through city-scale optical fibres. The atomic ensembles function as quantum memories that store quantum states. We use cavity enhancement to efficiently create atom-photon entanglement^13-15 and we use quantum frequency conversion¹⁶ to shift the atomic wavelength to telecommunications wavelengths. We realize entanglement over 22 kilometres of field-deployed fibres via two-photon interference^17,18 and entanglement over 50 kilometres of coiled fibres via single-photon interference¹⁹. Our experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the atomic quantum network, paving the way towards establishing atomic entanglement over many nodes and over much longer distances.